Conjunctivitis, also known as pink eye, is inflammation of the outermost layer of the white part of the eye and the inner surface of the eyelid.[1] It makes the eye appear pink or reddish. There may also be pain, burning, scratchiness, or itchiness. The affected eye may have increased tears or be "stuck shut" in the morning. Swelling of the white part of the eye may also occur.[2] Itching of the eye is more common in cases due to allergies.[3] Conjunctivitis can affect one or both eyes.[2]

The most common infectious causes are viral followed by bacterial.[3] The viral infection may occur along with other symptoms of a common cold. Viral and bacterial cases are easily spread between people.[2] Allergies to pollen or animal hair is also a common cause.[3] Diagnosis is often based on signs and symptoms. Occasionally a sample of the discharge is sent for culture.[2]

About 3 to 6 million people get conjunctivitis each year in the United States.[2][3] In adults viral causes are more common, while in children bacterial causes are more common.[3] Typically people get better in one or two weeks.[2][3] If there is visual loss, significant pain, sensitivity to light, signs of herpes, or a person is not improving after a week, further diagnosis and treatment may be required.[3] Conjunctivitis in a newborn, known as neonatal conjunctivitis, may also require specific treatment.[2]

Viral conjunctivitis is often associated with an infection of the upper respiratory tract, a common cold, and/or a sore throat. Its symptoms include excessive watering and itching. The infection usually begins with one eye, but may spread easily to the other.

Bacterial conjunctivitis causes the rapid onset of conjunctival redness, swelling of the eyelid, and mucopurulent discharge. Typically, symptoms develop first in one eye, but may spread to the other eye within 2–5 days. Bacterial conjunctivitis due to common pyogenic (pus-producing) bacteria causes marked grittiness/irritation and a stringy, opaque, greyish or yellowish mucopurulent discharge that may cause the lids to stick together, especially after sleep. Severe crusting of the infected eye and the surrounding skin may also occur. The gritty and/or scratchy feeling is sometimes localized enough for patients to insist they must have a foreign body in the eye. The more acute pyogenic infections can be painful.[citation needed] Common bacteria responsible for non-acute bacterial conjunctivitis are Staphylococci and Streptococci.[6]

Chemical eye injury is due to either an acidic or alkali substance getting in the eye.[7] Alkalis are typically worse than acidic burns.[8] Mild burns will produce conjunctivitis, while more severe burns may cause the cornea to turn white.[8]Litmus paper is an easy way to rule out the diagnosis by verifying that the pH is within the normal range of 7.0—7.2.[7] Large volumes of irrigation is the treatment of choice and should continue until the pH is 6—8.[8]Local anaestheticeye drops can be used to decrease the pain.[8]

Irritant or toxic conjunctivitis show primarily marked redness. If due to splash injury, it is often present in only the lower conjunctival sac. With some chemicals, above all with causticalkalis such as sodium hydroxide, there may be necrosis of the conjunctiva with a deceptively white eye due to vascular closure, followed by sloughing of the dead epithelium. This is likely to be associated with slit-lamp evidence of anterior uveitis.

Inclusion conjunctivitis of the newborn (ICN) is a conjunctivitis that may be caused by the bacteria Chlamydia trachomatis, and may lead to acute, purulent conjunctivitis.[9] However, it is usually self-healing.[9]

Conjunctivitis is identified by irritation and redness of the conjunctiva. Except in obvious pyogenic or toxic/chemical conjunctivitis, a slit lamp (biomicroscope) is needed to have any confidence in the diagnosis. Examination of the tarsal conjunctiva is usually more diagnostic than the bulbar conjunctiva.

Conjunctivitis when caused by an infection is most commonly caused by a viral infection.[10] Bacterial infections, allergies, other irritants and dryness are also common causes. Both bacterial and viral infections are contagious and passed from person to person, but can also spread through contaminated objects or water.

Cultures are not often taken or needed as most cases resolve either with time or typical antibiotics. Swabs for bacterial culture are necessary if the history and signs suggest bacterial conjunctivitis but there is no response to topical antibiotics. Viral culture may be appropriate in epidemic case clusters.

A patch test is used to identify the causative allergen in the case where conjunctivitis is caused by allergy.[18]

There are more serious conditions that can present with a red eye such as infectious keratitis, angle closure glaucoma, or iritis. These conditions require the urgent attention of an ophthalmologist. Signs of such conditions include decreased vision, significantly increased sensitivity to light, inability to keep eye open, a pupil that does not respond to light, or a severe headache with nausea.[19] Fluctuating blurring is common, due to tearing and mucoid discharge. Mild photophobia is common. However, if any of these symptoms are prominent, it is important to consider other diseases such as glaucoma, uveitis, keratitis and even meningitis or carotico-cavernous fistula.

A more comprehensive differential diagnosis for the red or painful eye includes:[19]

Bacterial conjunctivitis usually resolves without treatment.[10] Topical antibiotics may be needed only if no improvement is observed after three days.[23] In people who received no antibiotics, recovery was in 4.8 days, with immediate antibiotics it was 3.3 days, and with delayed antibiotics 3.9 days. No serious effects were noted either with or without treatment.[24] As they do speed healing in bacterial conjunctivitis, their use is also reasonable.[25]

In those who wear contact lenses, are immunocompromised, have disease which is thought to be due to chlamydia or gonorrhea, have a fair bit of pain, or who have lots of discharge, antibiotics are recommended.[10] Gonorrhea or chlamydia infections require both oral and topical antibiotics.[10]

When appropriate, the choice of antibiotic varies, differing based on the cause (if known) or the likely cause of the conjunctivitis. Fluoroquinolones, sodium sulfacetamide, or trimethoprim/polymyxin may be used, typically for 7–10 days.[11] Cases of meningococcal conjunctivitis can also be treated with systemic penicillin, as long as the strain is sensitive to penicillin.

When investigated as a treatment, Povidone-iodine ophthalmic solution has also been observed to have some effectiveness against bacterial and chlamydial conjunctivitis, with a possible role suggested in locations where topical antibiotics are unavailable or costly.[26]

Conjunctivitis due to chemicals is treated via irrigation with Ringer's lactate or saline solution. Chemical injuries (particularly alkali burns) are medical emergencies, as they can lead to severe scarring and intraocular damage. People with chemically induced conjunctivitis should not touch their eyes, regardless of whether or not their hands are clean, as they run the risk of spreading the condition to another eye.